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Two metal wires of identical dimensions are connected in series. If σ1 and σ2 are the conductivities of the metal wires respectively, the effective conductivity of the combination is:

1. 2σ1σ2σ1+σ2 2. σ1+σ22σ1σ2
3. σ1+σ2σ1σ2 4. σ1σ2σ1+σ2

Subtopic:  Derivation of Ohm's Law |
 64%
From NCERT
NEET - 2015
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A potentiometer wire of length L and a resistance r are connected in series with a battery of EMF E0 and resistance r1. An unknown EMF is balanced at a length l of the potentiometer wire. The EMF E will be given by:
1. LE0rlr1
2. E0r(r+r1)lL
3. E0lL
4. LE0r(r+r1)l

 76%
From NCERT
NEET - 2015
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A potentiometer wire has a length of 4 m and resistance  8 Ω.  The resistance that must be connected in series with the wire and an energy source of emf 2 V, so as to get a potential gradient of 1 mV per cm on the wire is:
1. 32 Ω
2. 40 Ω
3. 44 Ω
4. 48 Ω

 65%
From NCERT
NEET - 2015
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A,B and C are voltmeters of resistance R, 1.5R and 3R respectively as shown in the figure above. When some potential difference is applied between X and Y, the voltmeter readings are VA, VB and VC respectively. Then:

        

1. VA=VB=VC 2. VAVB=VC
3. VA=VBVC 4. VAVBVC

Subtopic:  Kirchoff's Voltage Law |
 65%
From NCERT
NEET - 2015
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Across a metallic conductor of non-uniform cross-section, a constant potential difference is applied. The quantity which remains constant along the conductor is:
1. current density 2. current
3. drift velocity 4. electric field
Subtopic:  Current & Current Density |
 61%
From NCERT
NEET - 2015
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Two cities are 150 km apart. The electric power is sent from one city to another city through copper wires. The fall of potential per km is 8 volts and the average resistance per km is 0.5 ohm. The power loss in the wire is:
1. 19.2 W
2. 19.2 kW
3. 19.2 J
4. 12.2 kW

Subtopic:  Heating Effects of Current |
 83%
From NCERT
AIPMT - 2014
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The figure given below shows a circuit when resistances in the two arms of the meter bridge are 5 Ω and R, respectively. When the resistance R is shunted with equal resistance, the new balance point is at 1.6l1. The resistance R is: 
           
1. 10 Ω
2. 15 Ω
3. 20 Ω
4. 25 Ω

Subtopic:  Meter Bridge |
 73%
From NCERT
AIPMT - 2014
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A potentiometer circuit has been set up for finding the internal resistance of a given cell. The main battery, used across the potentiometer wire, has an emf of 2.0 V and negligible internal resistance. The potentiometer wire itself is 4 m long. When the resistance, R, connected across the given cell, has values of (i) infinity (ii) 9.5, the 'balancing lengths, on the potentiometer wire, are found to be 3 m and 2.85 m, respectively. The value of the internal resistance of the cell is (in ohm):
1. 0.25
2. 0.95
3. 0.5
4. 0.75

 65%
From NCERT
AIPMT - 2014
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A wire of resistance 4 Ω is stretched to twice its original length. The resistance of a stretched wire would be:

1. 4 Ω 2. 8 Ω
3. 16 Ω 4. 2 Ω
Subtopic:  Derivation of Ohm's Law |
 84%
From NCERT
AIPMT - 2013
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The internal resistance of a 2.1 V cell which gives a current of 0.2 A through a resistance of 10 Ω is:
1. 0.5 Ω
2. 0.8 Ω
3. 1.0 Ω
4. 0.2 Ω
Subtopic:  EMF & Terminal Voltage |
 85%
From NCERT
AIPMT - 2013
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